Nitric oxide (NO) in the kidney plays a critical role in the regulation of fluid and electrolyte balance and blood pressure. It has been widely accepted that both the production of NO and NO-dependent effects, are independent of extracellular L-arginine and cellular L-arginine uptake; yet a series of recent studies from our laboratory and other laboratories has provided reason to question this view. These studies have demonstrated that supplementation of L-arginine, the substrate for NO synthase (NOS), directly into the renal medulla prevents sodium sensitive hypertension in the Dahl salt-sensitive (SS/Mcw) rat. Further experiments indicate that the cellular availability of L-arginine can regulate the production of NO and reactive oxygen species (ROS) in the kidney. We hypothesize that a deficiency in the L-arginine-nitric oxide pathway in the tubular and vascular segments of the kidney of the Dahl SS/Mcw rat contributes to the development of sodium-sensitive hypertension by reducing the availability of NO and/or increasing the levels of ROS. We will test this hypothesis in three Specific Aims. Aim 1 will utilize cellular and molecular techniques to quantify the differences in L-arginine uptake in whole tissue and isolated renal tubules and blood vessels of the SS/Mcw rat in comparison to control rats. Further studies in this aim will characterize the influence of altered L-arginine uptake mechanisms on NO release in renal tubules and blood vessels of the SS/Mcw rat. Aim 2 will employ novel in vivo microdialysis techniques to determine if the deficiency in L-arginine transport contributes to the decreased availability of NO and elevation in free radicals observed in the kidney of the SS/Mcw rat. Moreover, it will be determined if increased cellular L-arginine uptake will normalize the levels of NO and ROS in the SS/Mcw rat. Experiments in Aim 3 will then determine the effects on renal function and arterial blood pressure when NO and ROS levels in the kidney are manipulated by altering cellular L-arginine uptake. Studies in this aim will describe the in vivo effects of manipulation of cellular L-arginine uptake on the acute pressure-natriuresis-diuresis relationship, intrarenal blood flow distribution, and the long-term regulation of fluid and electrolyte balance and arterial blood pressure in SS/Mcw and control rats. Together, this integrated approach will determine the important role of cellular arginine uptake by cationic amino acid transporters (CAT) in the production of NO and ROS in the kidney, the regulation of renal sodium excretion, and the long-term control of arterial blood pressure in the Dahl SS/Mcw rat. Results of these studies should provide novel insights into the role of cationic amino acid transport in the control of renal function and arterial blood pressure. Moreover, these results may reveal that altering the dietary amino acid content and/or manipulating L-arginine uptake mechanisms may reduce the incidence of hypertension in the general population.